The present invention is directed to a device for cutting undercuts in a borehole formed in a material into which the borehole is drilled with the device including a housing bearing against the surface of the material with a guide sleeve located in a bore through the housing. The guide sleeve has an eccentric bore parallel with the bore in the housing and a bushing is positioned within the guide sleeve bore and has an eccentric bore therethrough. The bushing can be rotated through an angle of approximately 180.degree. degrees relative to the guide sleeve. A drive shaft extends through the eccentric bore in the bushing and has a cutter head at one end and can be coupled at the opposite end to a driving device. A blocking member extends from the housing into contact with the guide sleeve so that the guide sleeve can be rotated only in one direction relative to the housing.
Undercuts in bores are produced mainly for receiving correspondingly designed anchor dowels which can be anchored in a positively locked manner in the undercut. Due to the costly methods of fabricating undercuts or the malfunction-prone devices for carrying out the methods, up to the present time such dowels have not been used to any great extent.
A drilling device for cutting undercuts in boreholes is disclosed in EP-A 0 231 720, however, it is relatively cumbersome to handle. In this device the eccentricity of the guide sleeve corresponds to that of the eccentric bushing. As a result, the drive shaft is arranged centrally in the guide sleeve in one end position of the guide sleeve and the eccentric bushing, in the other end position of the eccentric bushing rotated through an angle of 180.degree., the drive shaft is pressed radially outwardly against the surface of the borehole by twice the amount of the eccentricity with the cutting head penetrating into the material containing the borehole. With such penetration, the eccentric bushing and the guide sleeve are turned together through an angle of at least 360.degree.. As a result, a circumferentially extending undercut is produced in the borehole wall. Subsequently, the eccentric bushing is rotated further or in reverse through 180.degree. in the guide sleeve for positioning the drive shaft centrally in the guide sleeve so that the device can be removed from the borehole. Possible entrainment of the guide sleeve is prevented by a pin which can be extended or retracted manually. The pin is retracted when the eccentric bushing is to be turned relative to the guide sleeve for penetration into the borehole surface and is extended into the eccentric bushing for fabrication of a circumferentially extending undercut.
In DE-A 38 09 761 a blocking element is provided between the housing and the guide sleeve allowing the guide sleeve to turn only in one direction of rotation in the housing. The blocking element prevents entrainment of the guide sleeve when the eccentric bushing is rotated in the opposite direction. The blocking element, however, does not prevent entrainment of the guide sleeve during the rotational movement required for the penetration of the cutting head into the material containing the borehole.